This invention relates to a sewing machine wherein a needle and a workpiece are relatively moved to each other based on pattern data stored in advance in memory means for automatically forming a stitch pattern on the workpiece with a plurality of stitches formed by means of vertical movement of the needle.
In conventional automatic sewing machines of this type each position data of many stitches corresponding to desired pattern is consecutively stored as pattern data in memory means such as paper tapes, magnetic tapes, semiconductor memory means, etc., and the needle and the workpiece are relatively moved to each other based on the stored pattern data, while the needle is vertically reciprocated, to form a stitch pattern on the workpiece with many stitches. Therefore, the number of position data stored in the memory means, in the conventional machines, coincides with that of the all of the stitches. This brings about a great demerit, for example, preparing of pattern data even for a simple polygonal pattern requires that all of the pattern data regarding the all stitches are stored. As a result of this, the number of the pattern data to be stored amounts very large so as to occupy a lot of memory capacity in addition to a problematical time-consuming operation of working out the pattern data. Thus prepared pattern data can be used exclusively for a pattern of a predetermined size and shape. Even when forming a similar pattern in the whole configuration, but being dissimilar only in the stitch distance and the number of stitches, this pattern data can not be used at all. Separate pattern data adapted to the stitch distance and number must be prepared.
In the conventionally proposed sewing machines of this type of workholder for holding the workpiece is simply adapted to relatively move to the needle which is designed to move vertically alone. If therefore a stitch pattern requiring many zigzag stitches is formed on a workpiece, the workholder itself must be moved zigzag. For high speed zigzag movement of the workholder in case of rapidly forming zigzag stitches on the workpiece, a particular driving means such as a large capacity pulse motor capable of responding to the high speed is badly needed.